Continued Studies of Tuberculosis considered as a generation illness

My studies of tuberculosis as a generation illness have brought, I believe, some clarity to many obscure points around the course and behaviour of the disease, and as during the last couple of years, I have made further observations in this area I shall now allow myself to present these to the Society. Firstly, I must make some explanatory remarks. Ladies and gentlemen, as some of you will perhaps recollect from my previous lecture in spring of last year, these generation studies are built on five year groups, taking into account age groups and generations. It is known that, as a basis for these mortality values, lies the respective countries’ total population, and the generation groups begin thus with about 3.5 million children under five years of age in England’s case, 300,000 for both Denmark and for Norway, and with about 500,000 for Sweden. In addition, it can be further pointed out that all these mortality rates are calculated in the same way for all the countries. Of the last five year group (that for 1926-1930) we now know the tuberculosis mortality figures for 4 of these 5 years and it is the mean value here which is indicated with a broken line on my graphs. Before I go into detail about what the generation graphs themselves can tell us, I shall first allow myself to show a table (Table 1) which, in Norway’s case, shows the mortality relationships, before, during and after the characteristic decline in deaths from tuberculosis, which as we know began during infancy and early childhood in 1900-1905. On the uppermost line, marked as A: mortality rates per 10,000 during the first 5 years of life from 1871–1875 to 1926–1930; on the lower line marked as B: the corresponding values during 20 to 25 years of age from 1891–1895 to 1926–1930. The inclined arrows then indicate the values corresponding to the same generations. For infancy and early childhood years we find high and steady values, lying between 31.6 and 37.2 per 10,000 until 1901–1905 when the drop to 20.0 per 10,000 starts, and later continues to 9.4 per 10,000 during 1926–1930. For the age groups 20–25 years of age we also show here high and steady values, lying between 42.3 per 10,000 and 47.4 per 10,000 from 1891–1895 and the same for the 1921–1925 period; as it was first then that a smaller drop from 45.0 per 10,000 to 42.8 per 10,000 appears and then for the five year period afterwards we see a considerable drop to 31.5 per 10,000. During the twenty years from 1901–1920, it appears therefore that the tuberculosis mortality for adults seems not to be influenced by the prophylaxis which seemingly must be considered as one of the most important factors for the large and steady decline of the child mortality rate which takes place during the same two decades. And vice versa, the real decline in mortality for the age group 20–25 first takes place when the generations from 1900–1910, with their declining values from age group to age group, have reached adulthood. Thus, this notable drop for the adults in the 1920’s to 1930’s neither comes too early nor too late. Can one, by objective consideration of these facts, find any better explanation for this than to assume that these tuberculosis mortalities descried here, for the age groups 20–25, cannot have been primary infections that have occurred in adulthood but must, in the main, arise from infections during childhood, as the mortality for this population group as adults first starts to decline from that time when they have been replaced by less and less seriously affected generations? This view should at least be kept in mind during my presentation. And now I will proceed to describe the generation curves as they now exist. We start with Norway (fig. 1) as we have more knowledge about the generations here and we see, as previously mentioned, how these mortality curves decline steadily in an almost schematic way, follow each other from age group to age group, and what is especially noticeable is the law-directed course of the diagrams, as each curve clearly shows both to what The quality of the original figure/ did not permit better reproduction. The figure/ is/ are available in the electronic version of this paper at International Journal of Epidemiology online. 1 Lecture at the Norwegian Society for Medicine, published Norwegian Journal of Medicinal Science, vol 93, 1932. 2 Translated by Joan Linden Kristiansen, Fredrikstad, Norway. Published by Oxford University Press on behalf of the International Epidemiological Association